The nyala (Nyala angasii or Tragelaphus angasii), also called inyala,[3] is a spiral-horned antelope native to southern Africa. It is a species of the family Bovidae and genus Nyala, also considered to be in the genus Tragelaphus. It was first described in 1849 by George French Angas. The body length is 135–195 cm (53–77 in), and it weighs 55–140 kg (121–309 lb). The coat is rusty or rufous brown in females and juveniles, but grows a dark brown or slate grey, often tinged with blue, in adult males. Females and young males have ten or more white stripes on their sides. Only males have horns, 60–83 cm (24–33 in) long and yellow-tipped. It exhibits the highest sexual dimorphism among the spiral-horned antelopes.

The nyala is mainly active in the early morning and the late afternoon. It generally browses during the day if temperatures are 20–30 °C (68–86 °F) and during the night in rainy season. As a herbivore, the nyala feeds upon foliage, fruits and grasses, with sufficient fresh water. A shy animal, it prefers water holes rather than open spaces. The nyala does not show signs of territoriality, and individual areas can overlap each other. They are very cautious creatures. Old males live alone, but single sex or mixed family groups of up to 10 individuals can be found. These inhabit thickets within dense and dry savanna woodlands. The main predators of the nyala are lion, leopard and Cape hunting dog, while baboons and raptorial birds hunt for the juveniles. Mating peaks during spring and autumn. Males and females are sexually mature at 18 and 11–12 months of age respectively, though they are socially immature until five years old. After a gestational period of seven months, a single calf is born.

The nyala is the second taxon to branch off of the spiral-horned antelope family tree just after the lesser kudu. As the nyala line has remained separate for a considerable amount of time (over 5 million years), it has now been placed in its own monotypic genus Nyala. Nyala, like Ammelaphus (lesser kudu), was proposed by Edmund Heller, an American zoologist, in 1912[6] but not widely recognized, and was only re-established as a valid genus in 2011 by Peter Grubb and Colin Groves.[7] While Nyala is the accepted genus, other authors consider the nyala a species of Tragelaphus.[3]

Fossil evidence suggests that the nyala has been a separate species since the end of the Miocene (5.8 million years ago). Genetic evidence suggests that the proto-nyala had some early hybridization with the proto-lesser kudu, but the two have remained separate long after this crossing.[4]

The nyala is a spiral-horned and middle-sized antelope, between a bushbuck and a kudu.[10] It is considered the most sexually dimorphic antelope.[2] The nyala is typically between 135–195 cm (53–77 in) in head-and-body length.[2] The male stands up to 110 cm (43 in), the female is up to 90 cm (3.0 ft) tall. Males weigh 98–125 kg (216–276 lb), while females weigh 55–68 kg (121–150 lb). Life expectancy of the nyala is about 19 years.[11]

The coat is rusty or rufous brown in females and juveniles. But it grows a dark brown or slate grey in adult males, often with a bluish tinge.[2] Females and young males have ten or more white vertical stripes on their sides. Other markings are visible on the face, throat, flanks and thighs. Stripes are very less or absent in males. Both males and females have a white chevron between their eyes, and a 40–55 cm (16–22 in) long bushy tail white underside. Both sexes have a dorsal crest of hair running right from the back of the head to the end of the tail. Males have another line of hair along the midline of their chest and belly.[11][12]

Only the males have horns. Horns are 60–83 cm (24–33 in) long and yellow-tipped. There are one or two twists.[2] The spoor is similar to that of the bushbuck, but larger. It is 5–6 cm (2.0–2.4 in) long. The feces resemble round to spherical pellets.[13] The nyala has hairy glands on its feet, which leave their scent wherever it walks.[3]

The condition of the nyala often varies between the sexes. According to a study, this can be attributed to the differences in their body sizes. It was noted that during nutritional stress, old adults died in more numbers, of which most were males.[14] During an attempt of blood sampling in the nyala, it was found that Vitamin E levels varied during stress.[15]

The nyala can also suffer from myopathy. In between January 1973 and June 1981, 21 nyalas succumbed to the disease. The main symptoms were stiffness, inability to rise, and failure to suckle in newborns. Necrosis (that is, the premature death of cells in a living tissue) and mineralization were found in the skeletal muscle after a histological analysis. In the juveniles there was acute necrosis of the cardiac muscle. In adults, there was interstitial fibrosis of the cardiac muscle, along with arteriosclerosis.[20]

In a report published in 1994 entitled "Epidemiological observations on spongiform encephalopathies in captive wild animals in the British Isles" it was noted that spongiform encephalopathy (BSE) had been diagnosed in one nyala captive in a zoo.[21] The nyala was formerly affected by the disease rinderpest, although the viral disease is considered eradicated now.[1]

The nyala is active mainly in the early morning and late afternoon. It browses during the day if temperatures are 20–30 °C (68–86 °F) and during the night in rainy season.[22] These antelopes rest in thick bushes during the hot hours of the day.[2] The nyala is very shy and cautious in nature, and like remaining hidden rather than coming out in the open. Most sightings of the nyala in the wild are at water holes.[2] But now-a-days they are becoming less shy and often come out in the sight of tourists.[3]

Nyala groups are according to sex or mixed. Herds usually browse and drink water together.[10] Each group consists of two to ten individuals. A study in Zinave National Park at Mozambique showed that 67% of the observations were of groups of one to three nyalas, and the rest of the herds consisted of up to 30 nyalas. It was also seen that herds often broke up and formed again.[22] Generally adult males remain alone. Females often remain near their mothers when they have their offspring, so the relationships in female herds may be considered relatively closer than that of males.[11][23]

Alert and wary in nature, the nyala use a sharp, high, dog-like bark to warn others in a group about danger. This feature is mainly used by females.[11] They also react to the alarm calls of impala, baboon and kudu. The impala has been found to react to the calls of the nyala too.[11] The main predators of nyala are lion, leopard and Cape hunting dog, while baboons and raptorial birds are the predators of juveniles.[22][24]

As a herbivore, the nyala's diet consists of foliage, fruits, flowers and twigs. During the rainy season they feed upon the fresh grass. They need a regular intake of water, and thus choose places with a water source nearby. However, they are adapted to live in areas with only a seasonal availability of water.[11] A study in Zululand showed that the nyala fed mainly in the early morning and the late afternoon.[25] They feed at night during the rainy season.[24]

A study made in Mkhuze Game Reserve and Ndumu Game Reserve in Natal, focused on the dietary habits of the impala and the nyala, showed that the amount of dicotyledons in their diets varied seasonally. In the diet of nyala its content was 83.2% and impala's diet contained a lesser figure of 52% dicotyledons. The diet grew richer in fiber content and dietary proteins were less. The reverse occurred in the rainy season. As the rainy season arrived, both the species took to a diet of mainly monocotyledons, and the impala consumed more of them. The diet contained more proteins than fibers.[26]

Another study was done to find whether the sexual dimorphism in the nyala influenced its foraging habits. Vegetation surveys were conducted with the end of each feeding bout. It was found that females spent equal periods of time foraging in all the three habitats, but males preferred sand forest more. More differences were noted, as males ate woody species at a greater average height whereas females fed from the low herbaceous layer. It was concluded that the differences resulted from varying nutritional and energetic demands according to their diverse body sizes and differing reproductive strategies.[27]

The nyala breeds throughout the year, but mating peaks in spring and autumn. The reason for this is still unknown, but attributed to the photoperiod and the feeding habits of the animal.[28] Females reach sexual maturity at 11 to 12 months of age and males at 18 months (though they are socially immature until five years old).[2] Once sexually mature, a male's seminiferous tubules begin spermatogenesis, that is, the generation of sperm. In a study, males over 14 months old showed active spermatogenesis.[29]

Before ovulation, the Graafian follicles reach a length of at least 6.7 cm (2.6 in).[29] A female's estrus cycle is about 19 days long. Males mate with the female for two days of the cycle, but she allows it for only six hours per cycle. When the male enters a females' herd during mating, he makes a display by raising his white dorsal crest, lowering his horns and moving stiffly. As in many other animals, the males fight over dominance during mating.[11]

In a study, the Kidney Fat Indices (KFIs) of impalas and nyalas were studied to understand the influence of social class and reproduction on them. Kidney Fat Index is a technique in which the kidney is removed and weighed with the fat and once again excluding the fat. The resultant difference is the amount of fat on the kidney. The more the fat, the healthier the animal.[30] In rut, the male nyalas had less KFIs, that did not vary much with the season. Pregnant females, both the antelopes nyala and impala, had higher KFIs than the non-pregnant ones.[31]

There is a significant increase in corpus luteum in the last third of gestation.[29] Gestation is of seven months. A single calf is born, weighing 5 kg (11 lb). Birth takes place generally away from the sight of predators, in places like a thicket. The calf remains hidden for up to 18 days, and the mother nurses it in regular intervals. The calf remains with its mother till the birth of the next calf, during which males in rut drive it away from the mother.[11]

Nyalas choose places with fresh water sources nearby for their habitat.

The nyala inhabits dense lowland woodlands and thickets, mainly in southern Malawi, Mozambique, Zimbabwe, and eastern South Africa. It chooses places with good quality grasslands as well as provision of fresh water.[11] They also inhabit lush green river country.[3] The nyala's natural range stretches across southeast Africa from the Lower Shire Valley in Malawi through Mozambique and Zimbabwe to eastern South Africa and Swaziland.[1]

The geographic distribution of the nyala may be based on the genetic variation. According to a study of the nyala in South Africa, Mozambique, Malawi and Zimbabwe, a great difference was marked among the gene frequencies at three microsatelliteloci. Mitochondrial DNA analysis revealed the presence of a unique haplotype in individuals from each location. The conclusions were that the geographic variation in the nyala may be due to a distribution pattern based on the habitat specificity.[32]

The nyala have never been observed showing signs of territoriality. Territories overlap extensively, let it be of any sex.[22] The home ranges of males are approximately equal to that of females, about 10 km2. in area.[22]

The major threats to the population of the nyala are hunting, habitat loss, agriculture and cattle grazing.[1] Rinderpest outbreaks have also contributed in population loss.[1] This species is currently of Least Concern, and the population is considered stable by both the IUCN and CITES.[9] As of 1999, the total population of the nyala was around 32,000 individuals. More recent estimates show that South Africa has at least 30,000 nyalas, with 25,000 in KwaZulu-Natal. There are now more than 1,000 on protected areas and ranches in Swaziland. In Mozambique there are not more than 3,000, in Zimbabwe there are over 1,000 while numbers in Malawi have fallen from 3,000 to about 1,500. Namibia has the least population, about 250.[1]

Today over 80% of the total population is protected in national parks and sanctuaries, mostly in South African protected areas. These are the Ndumo Game Reserve, uMkuze Game Reserve and Hluhluwe-Umfolozi Game Reserve and Kruger National Park. 10 to 15% occur on private land. They mostly occur in South Africa due to the high demand for adult males as game trophies.[1]